1. Field of the Invention
The present invention relates to a focus detection device, an optical system that includes the focus detection device and a focus detection method.
2. Description of Related Art
Japanese Laid Open Patent Publication No. 2003-241075 discloses a focus detection device that detects the state of focal adjustment achieved with an optical system with focus detection light fluxes having passed through a pair of areas at the exit pupil plane of the optical system by utilizing a micro lens array. If a discrepancy manifests between the output levels of the pair of images formed with the pair of focus detection light fluxes, the device corrects the output levels of the pair of images so as to equalize them and then detects the extent of image offset based upon the pair of corrected image outputs.
However, in the related art, since-image information after photoelectric conversion is expanded or reduced, highly accurate detection of image offset can not be achieved if the output levels of the pair of images become greatly unbalanced owing to quantization or noise.